Hob for cutting roller-chain sprockets



Patented' Aug. v1930 -h .CARL OLSON, OI' CHICAGO, ILLINOIS,

'ASSIGNOB TO ILLINOIS TOOL WORKS, Ol'

OHICAGO, ILLINOIS, A CORPORATION Ol' ILLINOIS Inon non currmenoLLEn-cn'aI-N srnocxms application mea 'mgm as, m1. n `sarna no. 21am.

My invention relates to hobs for generating roller chain sprockets and one \of the ob'ects lof the invention isto .provide a hob w ich will-cut metal more freely than the hobs previously used, thereby enabling the hob to yield an increased output over' ordinary hobs and to make practical the cutting of roller chain sprockets of large pitch.

Another object is to provide a hob whichy at i lo any given moment will act upon the s rocket t'a greater number of points than cretoore. i

` Another object is to provide a hob that will take short chips or cuts at many points rath- 15, er than longer ch' s at fewer pomts, as in previously known hobs.

Another object is to` increase the smoothness of operationof the hob and distribute more widely the vstresses and strains incident to cutting, thereby relieving the strain on the machine and thus making it possible to feed the work faster and consequently incgease the output. 1-

Other characteristics which contribute to the foregoing objects' will become apparent from the following description taken in connection with the accompanying drawings lin which,

Figure 1 is a side view ofa hob en'ibodyingI ao the invention.

. producing. This particularsprock'et is-not of large pitch but in Figures 4 and 5. sprockets of larger pitch i e., fewer teeth in proportion to the diameter, are shown,`my hob having special utility in producing sprockets of 40 such character. y c

. Figures 4 and 5'are ews respectively vof known hobs and my new hob placed in juxta position for more thoroughly bringing out the contrast. f.

Like f numerals denote identical parts in the several figures. J i It is well known that roller chain sprockets as well as other forms of toothed gears imay be produced by the molding generating process by the employment of hobs. The teeth of the sprocket or otherl toothed member to be produced are laid out upon the basis of a circle which is concentricgwith the workand commonly termedl 'the generating circle.

This generating circle, as it will be herein- 55 after referred to, is .commonly coincident with, or approximately of the same diameter g as the pitch circle yof the work. i

I have .discovered thatfor the production of roller .chain sprockets the'vhob may be eo greatly improved by employing as the generating circle one which has a dlameter larger #than the overall diameter of the work.4 This produces a hob having a longer lead than in hobs usually employed .forithe purpose.`

I have found-'that by thus increasing the length ofthe lead the cutting action of the hob will be distributed over a greater arc of the work; 'willtake cuts at more points on the work, and will take cuts that are shorter 170 Ithan those taken by hobs of standard lead.

In order to give a'practical illustrationof -the difference between the Aimproved hoband those previously knownfI will first refer to Figure f1 in which is shown a hob ofconven- 75 tional form for. producing roller chain sprockets. In this view, as in Figure 5, the sprocket .'teeth A are of standard form, 'the valleys IO or bottom of theteeth spaces, being circular in profile. In both/views the broken line-12 represents the pitch circle of thesprooket and raccording to standard specications now employed in this countrv. this -nitch circle is approximately mid-height of the sprocket teeth. In the old form of hob, S5 the teethA B are developed upon a pitch line 14 whichfistangent to the pitch circle 12. In

) this' oldtvne hob the tops of the teeth. that is'. the portions lying outside of the pitch line,

- are circular in profile and almost are semi- 90 ycircles; this 4condition being illustrated by comparison with the dotted circlelG shown near the middle of Finire-4.

The c'onseduence is. that with this old tvpe of hob the teeth located near the centerof the hob takea .long cut. for illustration, a cut extending approximatelv from the point a: .through the point @fand to the point e. Figure 4. This 'cut extends almost throughout' a semi-circle with the result that the mid-poro tion of thehob is called upon-to do the major portion of the work whi e smaller cuts are takenat the points r and a. It will be undercircle ofthe sprocketwheel. These pro r- -aood am ingu f oes showI that the main, burden is imposed v upon the 'mid-portion" of the hob wit t re lLis merely illustrative of t ical conditions of the old style hob, but it chief burden imposed upon what may be re garded as the central tooth which cuts throughout an'arc of almost 180 degrees..

The result is that unless the cut is comparatively shallow it will cause undue-wear and tear upon the hob and the 'shock as the sucthe work will be confined to approximately three points on the gear blank and the l result is that the output of a hob of his character is of necessity limited. Now referring to` Figure. 5, which.illus tratesfthe form and-action of my new hob,- the teeth A. of the work remain -the same as ,before owing to the; fact that my hob is designed to .lroduce a sprocket of standard form. Th

ob, however, instead 'of being develo u n a pitch line 14 tangent -to the pitc circ e 12 is developed upon a Apitch line 18 tangent to a generatin circle 20 located considerably outsidef'of t e region conventionally considered in developing hobs for any1 purpose. n

' n the particular form illustrated this nerating circle 2O is considerably outside o the 'points ofthe sprocket teeth, in fact is shown tob'e approximately .as far .cutside of the points of. the sprocket teeth as -thepoints of the sprocket teeth are outside of the pitch tions 'may bevaried, but nevertheless, a ho of the proportions illustrated has `been found to give excellent results.

As a resultofincreasing the size of the generat' circle the lead ofthe hob is increased as wi be readily understood by those familiar with the theory f involute gearing.

To take a concrete exam le, for a sprocket of 1 pitch the lead o the ordinary hob of ay is about 1.517 inches owing to the fact that the links of a roller sprocket chain In addi/tion to this the are straight, whereas the measurement on the rocket is arcuate. But in a corresponding hob of my construction the lead is about 1.675 inches. I

As a result of this increased lead, the central tooth b1 of the new hob will take a much shorter cut at the valley of the teeth, bit will simultaneously take cuts at' the' points t, u near the intsof the adjacent s rocket teeth.

will take a cut at the int-1: on the adjacent sprocket4 to the eft'while the hob tooth b will take a cut at the adjacent tooth w `to the right. In otherA words, the new hob will contact and cut the work at live points,

simultaneously and each of these cuts will be of shorter length than the main or central cut iso in Figu cessive teeth take-hold .willbe excessive. A

' in this application,

toothV at the'lcfttaken by the old type hobs.V This has several advantages, for example, the work will 'be distributed over a.v greater length of the hob thusk increasingthe life of the hob and making it practical to take a somewhat deeper cut. The shock due to contact of the oncoming teeth will also be reduced and the action accordingly rendered smoother. The cutting action will also be spread over a greater arcuf ate length of the sprocket'. In ag egate, however, the lengths of the cuts wi l be as great as the aggregate lengths of cutl taken `y the oldtype of hob.

res 4 'of explanation shown hobs of than are employed in ractic'e, length at each end eiiig) surplusage,

greater length the additional p l but shown for the urpose' o the theory of construction and operation.

In' Figures 1 and 2, I have shown ahob of a length more apt -to be used in actual and 5, I have for the purpose etter illustrating v practice it being observed that a hob having a length 'of three teeth or three turns of the helix is suicient.

f It is desirable that the gashes 2O be helical instead ofstraight, in accordance with well 'known practice. It is also desirable that the teeth be hooked, that is be undercut slightly, to exert a shearing cut upon the work. It is goed practice tov provide an' eight per cent ook, approximately, although this may be varied without departing the invention. v

In orderto more clearly set forth the meaning of the term generating circle as used it might be stated that the generatin circle, when associated with the hobbing o sprocket teeth, is an imaginary circle whose circumference is e mallead of the hob times teeth to be generated in the sprocket. This circle therefore, the itch circle of the s rocket, as these circles in a rocket woul mean the root circle of the teet in one instance and a circle/passing through the center of the rollers in a chain wrapped around the sprocketl in/tlie other instance. The teeth of a certain characteristics which di er from the teethv of an involute gear in that the teeth of a sprocket are not generated from-a basic r of a system of gear teeth as is the case in developing involute gears. In fact, the curves in sprocket teeth are not necessarily involute curves, but are more or less arbitrary curves to comply with the rollers of a chain or an ag te contour of a chain wrapped on'and oilA 'e sprocket, certain portions of the teeth havi' clearances outside of the roller seat, while do not contact with the chain atI all but are merely guides forthe chain. `It will thus be apparent that by using the term generating circle applicant does not refer specifically to the base circle or the pitch circle -of the sprocket. 'Sprockets of any e number of yis not the base circle nor'` rocket have from the spirit of ualto the norizo' iso

arf/aes nurnber of teeth cannot be generatedV by the same basic rack as above pointed out, due to 'i the fact that the circular or arcuated pitch differ in sprockets of di'erent-diameters or v in different numbers of teeth even thou h the' pitch of the chain to runon thesersproc ets is thesame.'- J I have found that as result of thev construction hereinabove described the out ut of the high is oot ness of operation is'increasedfanda wider distribution, gaxi'ally, of stresses and `'strains is obtained.

Having thusdeseribedtmy invention what I'claim as new and desire .tol secure by Let- 1. A hob for cuttin I teeth is approximately oircular, said hob beenvelope t ing 'developed upon a pitch line corresponding to a nerating-'clrcle greater than-the pitch -circe of the sprocket.

' 2; A hob for sprockets, said hob avin its teeth arran ed according to a "helicoida thread and o a conteur to ro'vde a `short contact distance to e teeth of the i sprocket when the sprocket is rolling on a circle of a larger diamsprocket degrees `at` the, bottom of f Anstrich@ vof the hobibem'g tangent to a generatin sprockets, the' 'greater than the" itch of the `eter than the overall diameter of the sprocket.

'3. In a hojbfor nerating roller chain -s rockets and the-like having a helicoidal t read of a leadgreater than the circular pitchofthe sprocket te be cut, thepitch line 4. A* heb for generating feuef thais 'being 'greater-'t an the vpitch ofthe sprocket to be cut and ad'apted'to contact the spreek t at more than three separate' points simu unmask 1 l5. generating roller chain sprockets, thetplitch of the teeth' of l.thejliob an the pitch of them@ of the sprocket to 'be cut' and ada tact the sprocket 4at at least points simultaneously.A

' 6. A hob forv generating roller chain sprockets, the' helical lead ofthe heb being bein cut, the that the' roile o the hob teet being such ob tooth opposite the centerof the will engage an arc of less than 120 the tooth space on the sprocket and will simultaneously engage the sprocket teeth at other points remote from said arc.-

7 A hob' for generating roller chain sprockets, the helical lead of greater than the pitch of the cut, the profile o f the hob tee rocket tov be being: such rrocket"willengage an are of less than 120 greatly increased, its life prolonged,

roller chain sprockets wherein the'bottom othe space between the generating roller chain .generating circle, pandedlongitudinally Zand 'the sides of theitch of the teeth ofthe hob f chain sprockets said hob havin ve #evitaterocketto be lines of the sprocket the "hob Abeing hob tooth oppositethe center of the bottom ofthe tooth space on sprocketland' will simultaneouslyienga'ge l von the sprocket and will simultaneously en-l Space at points separate xfromjsaid gage the adacent side of the two teeth'adj a`I lcent to sai space at points separate from lsaid arc and willsimulta'neously engage* two other sprocket teeth.

9L A hob for generatin s rockets having k.ahelicoida thread,

utes at rightangles to the thread, teeth avingcuttin edges lying in the helicoidal thread, sai velope the profile of a roller chain to Ibe cut when generating on a circ greater 'diameter -than the sprocket, said thread havingrv a lead conformln ing exand' therefore l.

teeth sloping more gently than in the ordi#` nary hob and the undercut to increase the acuteness ofsai -cuttin edges.-

generating hoh for .cuttin roller aces ofthe teeth-bein so I reusachtige-f iralV 5- 'esl' I thread bemgcontigurated toens rocket A P le'cf chain sprockets, the teeth of said ho being conf urated so as toxca se them tog'ener'ate ,sproc et gear'teeth w en generating onza` circleof larger diameterthan thepitch cir# cle of the sprocket to becut.

arrangedaccording to ai helicoi th1ead-, and having its teeth sodconli'gura cause them to 'generate rocket gear teeth` 4when generati on a circ eof larger diameter than the pi` the front facci ofthe teeth undercut to increase thereof. v 12.' A `hob for said hob being deve opedupon a itchline corres riding thant -e itc circle of the geerjte'be; cut.

circleof the. gearl be cut, g thgiacuteness' of the jim l i nerating-lgear .I

to a generatlngfcir e greater- 11. A generatinghob.. for cutting-i roller fi I its 'teeth tedlesi@ 1'3. A ob ffor'generating' sprockets an thelike having a correspondin toa-distance circle which between a pair of extend helicoidal thread-cfa lea 1 1 measuredA falo a 1s of greater-diameter than' t e', sprocket to be'lcut, said distancebein taken radial ch cle, said naginary lines through-'the pitch circle of the sprocket at distance between which isfequal cular pitch ofD the sprocket. i 5,

In witness whereof, Ifh'ave: hereuntc 'gub-V scribedmyname. 1 i

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